/// <summary>
/// Encode an OpenThings <see cref="Message"/>
/// </summary>
/// <param name="message">The <see cref="Message"/> message to encode</param>
/// <returns>A <see cref="IList{T}"/> of the encoded OpentThings message bytes</returns>
public IList <byte> Encode(Message message)
{
Crc16Ccitt crc16Ccitt = new Crc16Ccitt(0);
List <byte> encoded = new List <byte>
{
0, // Length
message.Header.ManufacturerId,
message.Header.ProductId,
0, // Pip Msb
0, // Pip Lsb
(byte)(message.Header.SensorId >> 16),
(byte)((message.Header.SensorId & 0xFF00) >> 8),
(byte)(message.Header.SensorId & 0xFF)
};
foreach (var record in message.Records)
{
encoded.Add((byte)record.Parameter.Identifier);
encoded.AddRange(record.Data.Encode());
}
encoded.Add(0);
var crcBytes = crc16Ccitt.ComputeChecksumBytes(encoded.Skip(5).ToArray());
encoded.AddRange(crcBytes.Reverse());
encoded[0] = (byte)(encoded.Count - 1);
return(encoded);
}
/// <summary>
/// Decode a <see cref="IList{T}"/> of bytes representing the OpenThings message payload
/// </summary>
/// <param name="payload">The OpenThings payload message bytes</param>
/// <param name="pidMaps">A mapping of PID to manufacture Ids to enable linear shift encryption decoding</param>
/// <returns>A decode <see cref="Message"/></returns>
public Message Decode(IList <byte> payload, IList <PidMap> pidMaps)
{
Crc16Ccitt crc16Ccitt = new Crc16Ccitt(0);
if (payload == null || payload.Count == 0)
{
throw new ArgumentOutOfRangeException(nameof(payload));
}
if (payload.Count < 11)
{
throw new OpenThingsException($"Invalid buffer length [{payload.Count}] too short");
}
if (payload[0] < 11)
{
throw new OpenThingsException($"Invalid OpenThings Header length [{payload[0]}]");
}
if (payload[0] > payload.Count)
{
throw new OpenThingsException($"Invalid OpenThings Header length [{payload[0]}] Buffer Length: [{payload.Count}]");
}
var pip = BitConverter.ToUInt16(payload.Skip(3).Take(2).Reverse().ToArray(), 0);
var header = new MessageHeader(payload[1], payload[2], pip, 0x0);
var body = payload.Take(payload[0] + 1).Skip(5).ToList();
if (pip != 0)
{
var pidMap = pidMaps.FirstOrDefault(_ => _.ManufacturerId == header.ManufacturerId);
if (pidMap == null)
{
throw new OpenThingsException($"No [{nameof(PidMap)}] found for manufacture id [0x{header.ManufacturerId:X}]");
}
body = Decrypt(body, pidMap.Pid, header.Pip);
header.SetSensorId(body.Take(3).ToList());
}
else
{
header.SetSensorId(body.Take(3).ToList());
}
ushort crcActual = (ushort)((body.Skip(body.Count - 2).First() << 8) + body.Skip(body.Count - 1).First());
ushort crcExpected = crc16Ccitt.ComputeChecksum(body.Take(body.Count - 2).ToArray());
if (crcActual != crcExpected)
{
throw new OpenThingsException($"Invalid Crc Expected: [0x{crcExpected:X4}] Actual: [0x{crcActual:X4}]");
}
var message = new Message(header);
ParseMessageRecords(message, body.Skip(3).Take(body.Count - 6).ToList());
return(message);
}